1. Field of the Invention
The present invention relates to a color selecting structure for a cathode-ray tube (CRT) and, more particularly, to damper wires (fine wires) extended on the tape surface of an aperture grille plate (AG) for a TRINITRON CRT, in which color phosphor stripes and provided and a single electron gun emits three beams, to prevent vibrations.
2. Description of the Prior Art
A TRINITRON CRT, in which color phosphor stripes are provided and a single electron gun emits three beams, uses, as a color selecting structure, a plurality of tape-shaped grid elements formed by a plurality of vertical apertures in a thin plate, such as a thin steel sheet, by an etching process and welded to a frame so as to extend tautly in a fixed tension. The thin plate, i.e., the etched thin plate, having the apertures, the plurality of tape-shaped grid elements and the framing elements is called a FAG (framing aperture grille plate). Electron beams pass through the apertures of the FAG and impinge on the fluorescent screen to make portions of the fluorescent screen luminous.
FIG. 2 is a perspective view of a FAG mounted on a frame, FIG. 3 is a sectional view taken on line I--I in FIG. 2, and FIG. 4 is an enlarged view of a portion of FIG. 2. Shown in FIGS. 2 to 4 are a frame 1, a FAG 2, tape-shaped grid elements 2a, apertures 2b, and two damper wires 3 extended perpendicularly to the apertures 2b to restrain the FAG from vibration, damper springs 4 fixedly holding the damper wires 3 on the frame 1. Usually, the damper wires 3 are tungsten wires of a diameter in the range of 10 to 30 .mu.m. As shown in FIG. 4, the tape-shaped grid elements 2a, i.e., strips of a soft steel, are arranged in parallel to each other and vibrate like the strings of musical instruments according to the length and tension thereof. The vibration of the grid elements 2a disturbs the landing of electron beams on the fluorescent screen, disturbing images formed thereon. Therefore, the damper wires 3 are extended perpendicularly to the grid elements 2a to restrain the grid elements 2a from vibration.
Although the higher the tension of the damper wires, the greater is the effect of the damper wires on the attenuation of the vibration of the aperture grille AG, the high tension of the damper wires entails a new problem. If each tape-shaped grid element 2a, which is a strip of a soft steel, is dislocated from a correct position 7a to an incorrect position 7b as shown in FIG. 5 by heat or mechanical shock applied thereto, it is possible that the dislocated tape-shaped grid element 2a is held firmly at the incorrect position 7b and unable to restore itself to its correct position 7a when the tungsten wire is extended excessively tautly. If an aperture grille having dislocated grid elements is put on the screen of a CRT, vertical moire fringes of fine pitches appear on the screen. These vertical moire fringes become conspicuous particularly when the entire screen is white.